Cut the watermelon into slim segments then into 5cm wedges. Preheat the oven to 240C/220C fan/gas 9. Arrange the watermelon in one or two roasting dishes, dot with the butter and season very lightly. Roast for 35-40 minutes, or until the fruit has given out most of its juices, stirring halfway through.

Towards the end, heat a large nonstick frying pan over a high heat. Season the chops on both sides and sear in batches until nicely golden, including the fat at the edges.

Drizzle the vinegar over the watermelon and give it a stir, loosening it with a spatula. Arrange the chops on top, scatter over a few rosemary needles, drizzle over the oil and return to the oven for 10 minutes. Leave to rest for 5 minutes. Spoon the pan juices over the lamb and watermelon before serving.